1. Field of the Invention
The invention relates to a coolant control device for controlling a cooling device that cools or warms up an internal combustion engine by circulating coolant.
2. Description of Related Art
In an existing art, there has been suggested a technique for circulating coolant in order to cool or warm up an internal combustion engine (engine). For example, Japanese Patent Application Publication No. 2009-150266 (JP 2009-150266 A) describes a technique for adjusting the ratio between the flow rate of coolant in a water jacket of an internal combustion engine and the flow rate of coolant in a bypass passage that bypasses the internal combustion engine when the internal combustion engine is warmed up. More specifically, JP 2009-150266 A describes a technique for circulating coolant in the bypass passage while stopping circulation of coolant in the water jacket at the time of warm-up of the internal combustion engine in order to facilitate the warm-up of the internal combustion engine. In addition, JP 2009-150266 A describes a technique for, in order to suffice the quantity of heat required by a heater core, at the time of warm-up of the internal combustion engine and when the quantity of heat required by the heater core is larger than the quantity of heat recovered by an exhaust heat recovery device, (i) stopping circulation of coolant in the bypass passage and circulating coolant in the water jacket or (ii) reducing the flow rate of coolant that circulates in the bypass passage and increasing the flow rate of coolant that circulates in the water jacket.
Another related art relating to the invention of the present application may be Japanese Patent Application Publication No. 2011-99400 (JP 2011-99400 A). JP 2011-99400 A describes a technique for, when there is no request to heat the inside of a vehicle cabin, circulating coolant in a coolant passage that bypasses an internal combustion engine while stopping circulation of coolant in a coolant passage that passes through the internal combustion engine by closing a relief valve. In addition, JP 2011-99400 A describes a technique for, in order to suffice a heating request, when there is a request to heat the inside of the vehicle cabin, circulating coolant in the coolant passage that passes through the internal combustion engine in addition to circulating coolant in the coolant passage that bypasses the internal combustion engine by opening the relief valve.
On the other hand, with the technique described in JP 2009-150266 A, when the quantity of heat required by the heater core is larger than the quantity of heat recovered by the exhaust heat recovery device, the flow rate of coolant in the bypass passage that passes through the exhaust heat recovery device is set to zero or reduced and then coolant flows into the water jacket of the internal combustion engine. Therefore, the flow rate of coolant flowing into the water jacket relatively easily increases, so the quantity of heat generated by the internal combustion engine is relatively easily drawn by coolant. Therefore, with the technique described in JP 2009-150266 A, there is a concern that the startability of the internal combustion engine deteriorates. Such deterioration in the startability of the internal combustion engine leads to deterioration in fuel economy.
Similarly, with the technique described in JP 2011-99400 A, when there is a heating request, the flow rate of coolant in the coolant passage that passes through the internal combustion engine significantly increases due to the opened relief valve. Therefore, the quantity of heat generated by the internal combustion engine is relatively easily drawn by coolant, so there is a concern that the startability of the internal combustion engine deteriorates. Such deterioration in the startability of the internal combustion engine leads to deterioration in fuel economy.